For their excellent electrical conductivity, thermal conductivity, sliding characteristics, mechanical characteristics and other characteristics, studies have been made on fibrous carbon nanostructures such as carbon nanotubes (hereinafter occasionally referred to as “CNTs”) for use in a wide variety of applications.
These studies have led to recent efforts to develop a technology that provides composite resin materials having resin characteristics (e.g., workability and strength) combined with characteristics of fibrous carbon nanostructures (e.g., electrical conductivity) by exploiting such excellent characteristics of fibrous carbon nanostructures to form a composite of the fibrous carbon nanostructures and resin material.
Specifically, there have been proposed composite resin materials in which fibrous carbon nanostructures are dispersed and retained on the surface of a particulate resin material (hereinafter occasionally referred to as “resin particles”) (see, e.g., PTL 1 and PTL 2). The composite resin material described in PTL 1 is produced by a process including the step of mixing fibrous carbon nanostructures using ultrasonic waves for attachment on the surface of resin particles which have been swollen and softened in subcritical or supercritical carbon dioxide. With this production process, the fibrous carbon nanostructures are dispersed to cover almost the entire surface of the resin particles by the action of ultrasonic waves and are also firmly embedded within the resin particles from the surface toward the inside.
The composite resin material described in PTL 2 is produced by a process including the step of adsorbing fibrous carbon nanostructures on the surface of swollen, softened resin particles by gently stirring a mixed solution of the fibrous carbon nanostructures and resin particles in a subcritical or supercritical carbon dioxide atmosphere. With this production process, it is possible to produce composite resin particles without causing fragmentation of the fibrous carbon nanostructures.